1. Field of the Invention
The present invention relates to fast code acquisition methods based on signed-rank statistic. In more detail, it relates to novel detectors required for PN (PN) code acquisition in direct sequence spread spectrum (DS/SS) systems.
2. Description of the Related Art
When the receiver and transmitter in a DS/SS system start communicating each other, the local despreading PN code sequence should first be synchronized to the incoming spreading PN code sequence. The synchronization process is normally composed of two steps: code acquisition and tracking. The code acquisition is a process of successive decisions wherein the final goal is to bring the two code sequences into (at least) coarse time alignment within a fraction g of the chip duration Tc. After the successful code acquisition, a code tracking loop is used to synchronize the two code sequences even more accurately. In the present invention, the code acquisition problem is considered.
The basic unit in any acquisition receiver is a decision-making device; that is, a detector. The class of detectors can be classified as either coherent or noncoherent; according to the specific detection criteria, it can be classified into Bayes, Neyman-Pearson, and etc. In accordance with the present invention, the noncoherent Neyman-Pearson detector is considered.
In the conventional parametric detector, the variance of time-varying interference has to be estimated to decide the threshold of a detector. Small deviation of the estimated value from the real value, however, may lead to a significant performance degradation of the parametric detector. The nonparametric detector based on the sign statistic has been proposed recently for the PN code acquisition problem, whose threshold can be decided without first estimating the variance of interference.
Accordingly, it is therefore the object of the present invention to provide the novel nonparametric detectors, which may improve the performance of code acquisition system.